Regulation of the AGS3·Gαi signaling complex by a seven-transmembrane span receptor

Abstract

G-protein signaling modulators (GPSM) play diverse functional roles through their interaction with G-protein subunits. AGS3 (GPSM1) contains four G-protein regulatory motifs (GPR) that directly bind Gαi free of Gβγ providing an unusual scaffold for the "G-switch" and signaling complexes, but the mechanism by which signals track into this scaffold are not well understood. We report the regulation of the AGS3·Gα i signaling module by a cell surface, seven-transmembrane receptor. AGS3 and Gαi1 tagged with Renilla luciferase or yellow fluorescent protein expressed in mammalian cells exhibited saturable, specific bioluminescence resonance energy transfer indicating complex formation in the cell. Activation of α2-adrenergic receptors or μ-opioid receptors reduced AGS3-RLuc·Gαi1-YFP energy transfer by over 30%. The agonist-mediated effects were inhibited by pertussis toxin and co-expression of RGS4, but were not altered by Gβγ sequestration with the carboxyl terminus of GRK2. Gαi-dependent and agonist-sensitive bioluminescence resonance energy transfer was also observed between AGS3 and cell-surface receptors typically coupled to Gαi and/or Gαo indicating that AGS3 is part of a larger signaling complex. Upon receptor activation, AGS3 reversibly dissociates from this complex at the cell cortex. Receptor coupling to both Gαβγ and GPR-Gαi offer additional flexibility for systems to respond and adapt to challenges and orchestrate complex behaviors. © 2010 by The American Society for Biochemistry and Molecular Biology, Inc.